Bobbin and core assembly



March 1966 K. w. LITCHFIELD ETAL 3,238,435

BOBBIN AND CORE ASSEMBLY Filed Aug. 25, 1963 9 32 l I 38 34 IIIIIIIJ 14 "1;;; 37 35 40 INVENTORS.

Kenneth W. Litchfield BY Jamesfi. Sm:'1h Q Atty.

United States Patent 3,238,485 BOBBIN AND CORE ASSEMBLY Kenneth W. Litchfield, Chicago, and James A. Smith,

Brooktield, Ill., assignors t0 Automatic Electric Laboratories, Northlake, 111., a corporation of Delaware Filed Aug. 23, 1963, Ser. No. 304,045 2 Claims. (Cl. 336198) The invention relates generally to a coil bobbin and core assembly, and more particularly to arrangements for securing a core within a molded coil bobbin and for securing a residual element to the core when the assembly is used in an electromagnetic device.

The advent of the use of molded coil bobbins in quick release type electromagnetic devices, while advantageously allowing the coil to be wound on an integrally molded bobbin instead of on a core, also created two problems. The first of these problems involved the need for securing the core in the molded bobbin to prevent them from separating after assembly; the second involved the use of a residual element of non-magnetic material on the core to provide for quick release of an armature or other device upon destruction of the magnetic field in the core and the need for securing such an element to the core.

The arrangement disclosed in the copending application of Joseph E. Zerwic, Serial No. 24,930, filed April 27, 1960 (now US. Patent 3,106,669, issued October 8, 1963), provided one solution for the first of the above mentioned problems; but the solution necessitated the use of an element external to the bobbin and core and an objectionably large molded extension on the core itself. It also required several assembly steps.

Therefore, it is an object of the invention to provide a novel and improved molded coil bobbin and core design for securing the core within the bobbin.

It is a further object of the invention to provide an arrangement for mounting and securing a residual element on a core in quick release type electromagnetic device.

The invention features small molded projections on the inner surface of the hollow tubular portion of the molded bobbin and a groove in the core receiving the projections to secure the core within the bobbin.

The invention also features a depression in the core receiving a constricted portion of the hollow cylindrical portion of the residual element to secure the residual element to the core.

Other objects and features and a fuller understanding of the invention will be had by referring to the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is an elevated view of this embodiment of the invention with the molded bobbin and the residual element in half section.

FIG. 2 is an end view of the bobbin without the core inserted.

FIG. 3 is an exploded perspective with a portion of the bobbin cut away to show the core partially inserted and with the residual element in position for mounting on the core.

Referring to the drawing, reference character designates an integrally molded coil bobbin which may be formed of any plastic insulating material; reference character 11 designates a core piece which may be formed of magnetic iron; and reference character 12 designates a residual element which may be of brass or other nonmagnetic metal.

The molded bobbin 10 has a hollow tubular portion 21 with outer surface 26 on which a coil of wire may be wound between the two end flanges 29 and 30. The inner surface 22 of the tubular portion 21 has thereon, near the end with the flange 29, four small radial projections 23. The radial projections 23 are integrally molded on Patented Mar. 1, 1966 the bobbin 10 and are spaced apart on the circumference of the inner surface 22. The projections 23 have cylindrical bases 24 and semispherical tops 25.

The magnetic iron core 11 is received by the hollow tubular portion 21 of the bobbin 10. One end of the core 11 has a small chamfer 32 which enables the projections 23 on the bobbin 10 to ride up onto the circumferential surface 31 of the core 11 more easily. The circumferential surface 31 has, near the chamfered end, a narrow, shallow depression or groove 33 which encompasses the whole circumference of the core. The groove 33 has fiat sides 34 and a semicircular bottom 35 and is formed on the core 11 to receive the molded projections 23 on the bobbin 10.

The molded bobbin 10 and the magnetic iron core 11 are assembled as shown partially accomplished in FIG. 3. The end of the core 11 having the chamfer 32 is inserted into the hollow tubular portion 21 at the end of the bobbin 10 having the flange 30. As the core 11 is inserted deeper into the tubular portion 21, the projections 23 engage the chamfer 32 and ride up onto the surface 31 of the core 11. The core is further inserted until the projections 23 slip into the groove 33. When this has been done the core is secured in the bobbin and cannot be easily removed. This securing then has been accomplished by the improved design of the coil bobbin and core featuring the projections on the bobbin and the groove on the core.

The core 11 also has a fluted knurl 50 on the surface 31 near the end opposite the chamfer 32. The knurl engages the inner surface 22 of the tubular portion 21 of the bobbin 10 to retard rotary movement of the core 11 in the bobbin 10.

Between the knurl 50 and the end of the core 11 nearest the knurl is a wide, shallow depression 36. The form of the depression 36 causes that end of the core to be shaped somewhat like the head of a pop bottle when viewed from the side. The depression has four flat portions 37, 38, 39, and 40. The flat portion 37 comprises one side of the depression 36 and is nearest the end of the core and perpendicular to the surface 31. The flat portion 38 is the bottom of the depression 36 and is parallel to the surface 31. The flat portion 39 with the flat portion 40 comprises the other side of the depression and forms a bevel which is spaced apart from the flat portion 38.

The residual element 12 has a hollow cylindrical portion 41 with an open end 42 and a closed end 43. The open end 42 is received by the end of the core 11 having the depression 36. The constricted portion 44 of the cylindrical portion 41 is received by the depression 36 in the core 11 to secure the residual element on the core. The depression 36 on the core 11 has thus combined with the constricted portion 44 on the residual element 12 to provide an arrangement for mounting and securing the residual element on the core.

The assembly of the core 11 and residual element 12 is accomplished by fitting the open end 42 of the hollow cylindrical portion 41 over the end of the core 11 and then forming the constricted portion 44 by a crimping process. This could be done by hand with a crimping tool or by an automatic machine.

The above description discloses one embodiment of the invention, however it is to be understood that numerous changes in detail and structure may be made without departing from the scope of the invention as hereinafter claimed. For example, the groove receiving the projections on the bobbin could have sections which are not cut out, thus preventing the projections from sliding around the groove, securing the core against rotary motion in the bobbin, and eliminating the need for a knurl on the core.

3 What is claimed is: a 1. 'In a quick release electromagnetic device, a bobbin and core assembly comprising a cylindrical core of magnetic material having two ends and an external surface, said external surface having a pair of grooves therein, each of said grooves surrounding said core near one end, a molded coil bobbin having a hollow tubular portion with an internal surface, said internal surface having at least one radial projection thereon, said core received by said hollow tubular portion of said bobbin, said projection engaging said core in one of said grooves to lock said core in said bobbin, and a residual cap of non-magnetic material having a hollow cylindrical configuration with one open end and one closed end, a constricted portion on said open end, said cap being mounted over the end of said core with said constricted portion engaging said core in the other of said grooves to lock said cap on said core.

2. In an electromagnetic device, in combination:

a core of magnetic material having a generally cylindrical outer surface, and a coil bobbin of insulating material, preformed separately from said core, with a hollow tubular portion,

the radius of said outer surface of said core being suificiently less than the radius of the inner surface of said hollow tubular portion to enable said core to be slid-ably inserted into said tubular portion of said bobbin,

said bobbin having at least one projection extending radially inward from said internal surface, said projection being integral with said bobbin and adjacent one end thereof, the inner surface of said radial projection being spaced from the axis of said bobbin by an amount less than said external radius of said core,

said core having a groove in its outer surface spaced from the corresponding end of said core by a relatively narrow portion of said outer surface, said core being slidably inserted in said bobbin so that said projection rides up onto said narrow portion of said core surface and then snaps into said groove to fasten said core in said bobbin.

References Cited by the Examiner UNITED STATES PATENTS 478,147 7/1892 Webb 242-683 1,831,280 11/1931 Wright et al 336-210 X 2,146,835 2/1939 Mcrwin 242-683 2,220,610 11/1940 Miller 242-683 2,584,723 2/1952 Maekey 336-136 2,831,642 4/ 1958 Michatek 242-683 2,913,640 1l/1959 Edgarton 336-196 X FOREIGN PATENTS 71,383 10/ 1942 Czechoslovakia.

ROBERT K. SCHAEFER, Primary Examiner.

JOHN F, BURNS, ROBERT K. SCHAEFER, Examiners.

T. J. KOZMA, Assistant Examiner. 

1. IN A QUICK RELEASE ELECTROMAGNETIC DEVICE, A BOBBIN AND CORE ASSEMBLY COMPRISING A CYLINDRICAL CORE OF MAGNETIC MATERIAL HAVING TWO ENDS AND AN EXTERNAL SURFACE SAID EXTERNAL SURFACE HAVING A PAIR OF GROOVES THEREIN, EACH OF SAID GROOVES SURROUNDING SAID CORE NEAR ONE END, A MOLDED COIL BOBBIN HAVING A HOLLOW TUBULAR PORTION WITH AN INTERNAL SURFACE, SAID INTERNAL SURFACE HAVING AT LEAST ONE RADIAL PROJECTION THEREON, SAID CORE RECEIVED BY SAID HOLLOW TUBULAR PORTION OF SAID BOBBIN, SAID PROJECTION ENGAGING SAID CORE IN ONE SAID GROOVES TO LOCK SAID CORE IN SAID BOBBIN, AND A RESIDUAL CAP OF NON-MAGNETIC MATERIAL HAVING A HOLLOW CYLINDRICAL CONFIGURATION WITH ONE OPEN END AND ONE CLOSED END, A CONSTRICTED PORTION ON SAID OPEN END, SAID CAP BEING MOUNTED OVER THE END OF SAID CORE WITH SAID CONSTRICTED PORTION ENGAGING SAID CORE IN THE OTHER OF SAID GROOVES TO LOCK CAP ON SAID CORE. 